The Story Starts Here (rocket ship) option has been moved to the sub-menu accessed by selecting the More Passage Options (three horizontal dots) option.
As far as I know, the icon still exists in the newest web version of Twine 2. The menu that pops up when a passage is interacted with has changed, but make starting point of story is still an option, I do believe.
While the rocket ship icon itself has been remove, the Story Starts Here option (that that icon represented) still remains.